The study was led by Yasuo Ikeda, MD, of the Graduate School of Advanced Science and Engineering, Waseda University, Tokyo, Japan, and looked at 14,464 patients aged 60 to 85 years, presenting with hypertension, dyslipidemia, or diabetes mellitus recruited by primary care physicians at 1,007 clinics in Japan between March 2005 and June 2007, and were followed up for up to 6.5 years. Patients were randomized 1:1 to enteric-coated aspirin 100 mg/d or no aspirin in addition to ongoing medications. The composite primary outcome was death from cardiovascular causes, nonfatal stroke and nonfatal myocardial infarction.

The study was terminated early after a median follow-up of 5.02 years based on likely futility. In both the aspirin and no aspirin groups, 56 fatal events occurred. Patients with an occurrence of nonfatal stroke totaled 114 in the aspirin group and 108 in the no aspirin group; of nonfatal myocardial infarction, 20 in the aspirin group and 38 in the no aspirin group; of undefined cerebrovascular events, three in the aspirin group and five in the no aspirin group. Regression analyses indicated that the risk of a primary end point event was higher in men vs. women (parameter estimate, 0.34; HR, 1.41 [95 percent CI, 1.14-1.74]; P = .002).

The authors note that “there remains a possibility that the statistically nonsignificant reduction in the risk of death from cardiovascular causes, nonfatal stroke, and nonfatal myocardial infarction was due to the study being inadequately powered, rather than an absence of beneficial effect of aspirin. However, even if the result had become statistically significant through prolongation of the study, the clinical importance of aspirin in the primary prevention of cardiovascular events would have been less than originally assumed. Therefore, it appears that aspirin is unlikely to show a clinically important benefit in the overall population included in this study.” Moving forward, the authors plan to “conduct further analyses to establish whether aspirin had beneficial effects in particular subgroups of patients or if there were beneficial effects with respect to cancer prevention.”

J. Michael Gaziano, MD, MPH, FACC; Philip Greenland, MD, FACC, note in a related editorial comment that “information from these studies will help refine guidelines that currently reserve aspirin for higher-risk patients.” They add that “findings from these studies, with additional data about risks and other potential long-term benefits, such as reducing the risk of colorectal and other cancers, will prove helpful for clinical decision making involving the role of aspirin for primary prevention.”